Method for fabricating in-plane switching mode liquid crystal display device

ABSTRACT

A method for fabricating an LCD device includes forming an alignment layer and an overcoat layer substantially simultaneously. The method includes, coating a mixture of an alignment layer material and an overcoat layer material on a substrate and at least partially separating the overcoat layer material and the alignment layer material by the curing the mixture.

This application claims the benefit of Korean Patent Application No.P2003-95469, filed on Dec. 23, 2003, which is hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display (LCD) devices.More particularly, the present invention relates to a method forfabricating an In-Plane Switching (IPS) mode LCD device. Moreparticularly still, the present invention relates to a method forfabricating an IPS mode LCD device wherein an alignment layer and anovercoat layer are formed substantially simultaneously.

2. Discussion of the Related Art

As information technology continues to evolve, the demand for, anddevelopment of, various types of flat panel display devices (e.g.,liquid crystal display (LCD), plasma display panel (PDP),electroluminescent display (ELD), and vacuum fluorescent display (VFD))increases. Among the various types of flat panel display devices, LCDdevices are advantageously lightweight, dimensionally compact, consumerelatively low amounts of power during operation, display images at highresolution and high luminance, and can display images on a large-sizedscreen. Accordingly, LCD devices are widely used, for example, assubstitutes for Cathode Ray Tubes (CRTs) and find numerous applicationsin mobile devices as such notebook computers, portable telephones, andthe like, as well as in other application such as televisions andcomputer monitors.

A typical LCD device includes an LCD panel for displaying images and adriver for supplying driving signals to the LCD panel. The LCD panelgenerally includes first and second substrates bonded to, but spacedapart from, each to form a cell gap therebetween. The first and secondsubstrates are bonded together by a sealant material and a substantiallyuniform cell gap is maintained between the bonded substrates by thepresence of spacers. A liquid crystal layer is formed within the cellgap between the first and second substrates by injecting liquid crystalmaterial through an injection hole formed in the sealant material andinto the cell gap.

Generally, the first substrate (i.e., the TFT array substrate) supportsa plurality of gate lines spaced apart from each other at a fixedinterval and extending along a first direction, a plurality of datalines spaced apart from each other at a fixed interval and extendingalong a second direction perpendicular to the first direction so as tocross the plurality of gate lines, a plurality of pixel regions arrangedin a matrix pattern defined by crossings of the gate and data lines, aplurality of pixel electrodes arranged within the plurality of pixelregions, and a plurality of thin film transistors connected to the gatelines, the data lines, and the pixel electrodes for switching signalsfrom the data lines to corresponding pixel electrodes in response tosignals transmitted from the gate lines. An alignment layer is formedover the first substrate and is rubbed to align the liquid crystal layerin a predetermined manner.

Generally, the second substrate (color filter array substrate) supportsa black matrix layer that prevents light from being transmitted inregions corresponding to areas outside the pixel regions of the firstsubstrate, an R/G/B color filter layer for selectively transmittingpredetermined wavelengths of light, and a common electrode for producingimages. An alignment layer is also formed over the second substrate andis rubbed to align the liquid crystal layer in a predetermined manner.

Upon applying predetermined voltages to the pixel and common electrodesof the LCD panel described above, an electric field, vertically orientedwith respect to the first and second substrates, is generated to alteran arrangement of liquid crystal molecules within the liquid crystallayer. Upon altering the arrangement of liquid crystal molecules, lighttransmittance characteristics of the LCD panel are selectively alteredand an image can thus be expressed. The LCD panel described above has ahigh aperture ratio but undesirably displays images over a narrow rangeof viewing angles. To solve this problem, In-Plane Switching (IPS) modeLCD devices have been developed, in which common and pixel electrodesare both formed on the first substrate. Accordingly, IPS mode LCDdevices generate electric fields oriented parallel to the substrates.

FIG. 1 illustrates a plan view of one pixel of a first substrate in arelated art IPS mode LCD device. FIG. 2 illustrates a cross-sectionalview of a first substrate and an opposing second substrate taken alongline I-I′ of FIG. 1.

Referring to FIGS. 1 and 2, a plurality of gate and data lines 12 and24, respectively, are formed on a first substrate 10 a so as to crosseach other and define a plurality of pixel regions P. A common electrodeline 16 is formed adjacent to, and parallel with, the gate lines 12. Athin film transistor T, including a gate electrode 14, an active layer20, a source electrode 26, and a drain electrode 28, is formed at acrossing of the gate and data lines 12 and 24, wherein the sourceelectrode 26 extends from the data line 24, and the gate electrode 14projects from the gate line 12. A pixel electrode 30 is formed withinthe pixel region P so as to be parallel with the data line 24 andelectrically connected to the drain electrode 28. The pixel electrode 30includes a plurality of first pixel electrode parts and one second pixelelectrode part each arranged over the common electrode line 16. Thefirst pixel electrode parts are spaced apart from each other at a fixedinterval and extend along a first direction over the first substratewhile the second pixel electrode part electrically connects the firstpixel electrode parts to each other. Further, a common electrode 17 isformed between, and parallel to, each of the first pixel electrode partsso as to be electrically connected to the common electrode line 16. Thecommon electrode 17 includes a plurality of first common electrode partsarranged between the first pixel electrode parts and extending away fromthe common electrode line 16 in addition to one second common electrodepart electrically connecting the first common electrode parts to eachother. Outermost ones of the first common electrode parts within thepixel region P are spaced apart from the data line 24 by a predetermineddistance. Additionally, insulating layers 21 are formed between the dataand common electrode lines 24 and 16, respectively, and between thecommon electrode line 16 and the common electrode 17. Lastly, a firstalignment layer 60 a is formed over the entire surface of the firstsubstrate 10 a, including over the pixel electrode 30.

As shown in FIG. 2, the second substrate 10 b opposes the firstsubstrate 10 a and supports includes a black matrix layer 42, an R/G/Bcolor filter layer 44, an overcoat layer 52, and a second alignmentlayer 60 b. The black matrix layer 42 prevents light from beingtransmitted in regions corresponding to areas outside the pixel regionsof the first substrate 10 a and the R/G/B color filter layer 44dimensionally conforms to the pixel region P and selectively transmitspredetermined wavelengths of light. The overcoat layer 52 is formed onthe color filter layer 44 to planarize the topography of the colorfilter layer 44 and to prevent pigments within the color filter layer 44from diffusing into the liquid crystal layer 50, formed between thefirst and second substrates 10 a and 10 b. Lastly, the second alignmentlayer 60 b is formed over the entire surface of the second substrate 10b, including over the overcoat layer 52.

The first and second alignment layers 60 a and 60 b discussed abovealign liquid crystal molecules within the liquid crystal layer 50 alongpredetermined directions and are typically formed of a polymer materialsuch as polyamide, polyimide compound, PVA(Polyvinyl Alcohol), polyamicacid, or a photosensitive material such as PVCH(PolyvinylCinnamate),PSCN(PolysiloxaneCinnamate) or CelCN(CelluloseCinnmate)-based compound.The overcoat layer 52 discussed above is typically formed from any oneof a photosensitive resin or an acrylic resin.

Upon driving LCD devices having a common electrode formed over theentire surface of the second substrate, including over the black matrixand color filter layers, an electric field is generated that isvertically oriented with respect to the surface of the first and secondsubstrates. Accordingly, the common electrode is functionally equivalentto the overcoat layer 52 illustrated in FIG. 2. However, upon drivingIPS mode LCD devices, an electric field is generated that is parallel tothe surface of the first and second substrates. Because the commonelectrode 17 is formed on the first substrate 10, it is necessary toform the overcoat layer 52 on the second substrate 10 b.

A related art method for fabricating the second substrate 10 b shown inFIG. 2 will now be described in greater detail with respect to FIGS. 3Ato 3C.

Referring to FIG. 3A, a light-shielding layer is deposited on the secondsubstrate 10 b and selectively removed in regions corresponding to thepixel regions P (i.e., patterned) to form the black matrix layer 42.Next, photosensitive layers (not shown) are repeatedly deposited overthe entire surface of the second substrate 10 b, including over theblack matrix layer 42, and patterned to remain within predeterminedportions of the pixel regions P to form the R/G/B color filter layer 44.After the color filter and black matrix layers 44 and 42 are formed, acleaning process is performed to remove foreign materials from thesecond substrate 10 b.

Referring to FIG. 3B, a photosensitive resin or acrylic resin is coated(i.e., spin coated) over the entire surface of the second substrate 10b, including over the color filter and black matrix layers 44 and 42.The coated resin is then cured to form the overcoat layer 52.

Referring to FIG. 3C, after forming the overcoat layer 52, a polymermaterial such as polyamide, polyimide compound, PVA(Polyvinyl Alcohol),polyamic acid, or a photosensitive material such asPVCH(PolyvinylCinnamate), PSCN(PolysiloxaneCinnamate) orCelCN(CelluloseCinnmate)-based compound is coated (i.e., spin coated)over the entire surface of the second substrate 10 b, including over theovercoat layer 52, cured, and rubbed or irradiated with light to formthe second alignment layer 60 b.

Fabricating the related art IPS mode LCD device as described above,however, is disadvantageous because the overcoat layer and the secondalignment layer must be formed using separate coating (i.e.,spin-coating) processes. The necessity for separate process stepsundesirably increases the fabrication time and cost. Further, theminimum thickness of each of the overcoat and second alignment layers isdetermined by the characteristics of the coating processes (i.e.,spin-coating processes) by which they are formed. Therefore, thecombined thickness of the overcoat and second alignment layers canbecome undesirably thick and disadvantageously reduce the lighttransmittance characteristics of the IPS mode LCD device.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forfabricating an IPS mode LCD device that substantially obviates one ormore of the problems due to limitations and disadvantages of the relatedart.

An advantage of the present invention provides a method for fabricatingan IPS mode LCD device wherein a second alignment layer and an overcoatlayer are formed substantially simultaneously, beneficially decreasingthe fabrication time and cost.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a methodfor fabricating a LCD device may, for example, include coating a mixtureover a substrate, wherein the mixture contains an alignment layermaterial, suitable for forming an alignment layer, and an overcoat layermaterial, suitable for forming an overcoat layer, on a substrate; andcuring the mixture wherein, upon curing, the overcoat layer material andthe alignment layer material at least partially separate from within themixture to substantially simultaneously form an overcoat layer and analignment layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 illustrates a plan view of one pixel of a first substrate in arelated art IPS mode LCD device;

FIG. 2 illustrates a cross-sectional view of a first substrate and anopposing second substrate taken along line I-I′ of FIG. 1;

FIGS. 3A to 3C illustrate a related art process of fabricating an IPSmode LCD device;

FIGS. 4A to 4C illustrate a process of fabricating an IPS mode LCDdevice according to principles of the present invention; and

FIG. 5 illustrates a flow chart of the process of fabricating an IPSmode LCD device according to principles of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIGS. 4A to 4C illustrate a process of fabricating an IPS mode LCDdevice according to principles of the present invention. FIG. 5illustrates a flow chart of the process of fabricating an IPS mode LCDdevice according to principles of the present invention.

Referring to FIG. 4A, a substrate 70 having a color filter layer 72 anda black matrix layer 71 may be prepared and cleaned to remove foreignmaterials from the surface thereof. After the cleaning, a mixture 73containing a predetermined ratio of material suitable for forming anovercoat layer (i.e., overcoat layer material 73 a) to material suitablefor forming an alignment layer (i.e., alignment layer material 73 b) maybe prepared (see S1 of FIG. 5) and coated (e.g., via a spin coatingmethod) over to the surface of the substrate 70, including the colorfilter layer 72 and the black matrix layer 71 (see S2 of FIG. 5).

In one aspect of the present invention, the mixture 73 may be preparedby mixing solvents of the alignment layer material 73 b and solvents ofthe overcoat layer material 73 a together. According to principles ofthe present invention, the density of the overcoat layer material 73 amay be greater than the density of the alignment layer material 73 b. Inone aspect of the present invention, the mixture 73 may, for example,contain more overcoat layer material 73 a than alignment layer material73 b. For example, about 1% to about 10% of the mixture 73 may consistof the alignment layer material 73 b. Accordingly, the mixture 73 mayproduce an overcoat layer that is thicker than the alignment layer. Inone aspect of the present invention, the mixture 73 may produce anovercoat layer that is thick enough to substantially planarize thetopography of the color filter layer 72 and prevent pigment within thecolor filter layer 72 from diffusing into a subsequently provided liquidcrystal layer.

In one aspect of the present invention, the alignment layer material 73b may, for example, include at least one of a polymer material such aspolyamide, polyimide compound, PVA(Polyvinyl Alcohol) or polyamic acid,or a photosensitive material such as PVCH(PolyvinylCinnamate),PSCN(PolysiloxaneCinnamate) or CelCN(CelluloseCinnmate)-based compound,or the like. For example, the alignment layer material 73 b may beformed by adding amide-based polar solvent of 5%, such asNMP(N-Metal-2-pyrrolidone), to polyamic acid, wherein the polyamic acidmay be obtained by reacting a compound of acid anhydride and diaminewith a solvent.

In one aspect of the present invention, the overcoat layer material 73 amay, for example, include at least one of a photosensitive resin, anacrylic resin, or the like. For example, the overcoat layer material 73a may be formed by adding NMP material to a photosensitive resin, anacrylic resin, or the like.

Referring to FIG. 4B, upon initially being coated onto the substrate 70,the overcoat layer material 73 a may begin to separate from thealignment layer material 73 b due to the difference in density betweenthe overcoat layer material 73 a and the alignment layer material 73 b.Accordingly, the overcoat layer material 73 a, having the higherdensity, may sink toward the color filter layer 72 and the black matrixlayer 71 while the alignment layer material 73 b, having the lowerdensity, may float away from the color filter layer 72, thereby formingseparate layers.

Referring to FIG. 4C, after the mixture 73 is coated, the mixture 73 maybe cured (see S3 in FIG. 5). Curing the mixture 73 may increase the rateat which the overcoat layer material 73 a separates from the alignmentlayer material 73 b. In one aspect of the present invention, the curingmay comprise exposing the coated mixture 73 to heat in a heat treatment.In another aspect of the present invention, the curing may furthercomprise irradiating the heat treated mixture 73 with light (e.g.,ultraviolet light). As a result, an overcoat layer, formed of theovercoat layer material 73 a, and an alignment layer, formed of thealignment layer material 73 b may beneficially be formed substantiallysimultaneously. Moreover, the resultant overcoat and alignment layersmay be strongly adhered to each other, thereby increasing thereliability of the resultant LCD device.

After the overcoat material 73 a and alignment layer material 73 b havesubstantially separated from within the mixture 73, the alignment layer,formed of the alignment layer material 73 b, may be treated (e.g.,rubbed, irradiated with light, etc.) to effect a predetermined alignmentof liquid crystal molecules within a subsequently provided liquidcrystal layer. For example, if the alignment layer material 73 b of thealignment layer includes a polyamide, a polyamic compound, PVA(PolyvinylAlcohol), polyamic acid, or the like, the treatment may include arubbing treatment. If, however, the alignment layer material 73 b of thealignment layer includes a photosensitive material such asPVCH(PolyvinylCinnamate), PSCN(PolysiloxaneCinnamate), aCelCN(CelluloseCinnmate)-based compound, or the like, the treatment may,for example, include an ultraviolet irradiation treatment.

As described above, the principles of the present invention areadvantageous in the fabrication of LCD devices (e.g., IPS mode LCDdevices) because the overcoat layer and the alignment layer may besubstantially simultaneously fabricated from a single overcoatlayer/alignment layer material mixture. Because the two layers arefabricated substantially simultaneously, the amount of time and cost tofabricate the LCD device may be reduced. Additionally, the overcoatlayer/alignment layer material mixture may be coated over the substratewith a spin coating device traditionally used in forming the related artovercoat layer. Accordingly, the alignment layer need not be formedusing a separate coating device traditionally used for coating therelated art alignment layer, thereby further decreasing the fabricationcost.

By separating overcoat and alignment layer materials from a commonlycoated mixture, as opposed to separately forming the overcoat andalignment layers, an overcoat/alignment layer structure having increasedadhesive characteristics may be obtained, thereby increasing thereliability of the resultant device.

Moreover, the mixture 73 is coated onto the substrate 70 in a singlecoating (e.g., spin coating) step. Therefore, once suitably formedaccording to the principles of the present invention, the individualthicknesses of the overcoat and alignment layers of the presentinvention may be less than the individual thicknesses of the overcoatand alignment layers formed according to the related art method asdescribed above and may provide an IPS mode LCD device having increasedlight transmittance characteristics compared to that of the IPS mode LCDdevice of the related art.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for fabricating a liquid crystal display (LCD) device,comprising: coating a mixture on a substrate, the mixture including analignment layer material suitable for forming an alignment layer and anovercoat layer material suitable for forming an overcoat layer; and atleast partially separating the alignment layer material from theovercoat layer material within the mixture.
 2. The method of claim 1,wherein at least partially separating the alignment layer material fromthe overcoat layer material includes curing the mixture.
 3. The methodof claim 1, wherein the curing includes thermally treating the mixture.4. The method of claim 1, wherein the curing includes irradiating themixture with light.
 5. The method of claim 3, wherein the light includesUV light.
 6. The method of claim 1, wherein the density of the alignmentlayer material is different from the density of the overcoat layermaterial.
 7. The method of claim 6, wherein the density of the alignmentlayer material is less than the density of the overcoat layer material.8. The method of claim 1, wherein the alignment layer material includesone of polyamide, polyimide-based compound, PVA, polyamic acid, PVCH,PSCN, and a CelCN-based compound.
 9. The method of claim 1, wherein theovercoat layer material includes one of a photosensitive resin and aacrylic resin.
 10. The method of claim 1, wherein the mixture containsmore of the overcoat layer material than the alignment layer material.11. The method of claim 10, wherein the mixture contains between about1% and about 10% of the alignment layer material.
 12. The method ofclaim 1, wherein the coating includes spin coating the mixture on thesubstrate.
 13. The method of claim 1, further comprising, prior to thecoating, forming at least one color filter layer on the substrate. 14.The method of claim 1, further comprising, prior to the coating, forminga black matrix layer on the substrate.
 15. The method of claim 1,further comprising performing an aligning treatment on the alignmentlayer.
 16. The method claimed in claim 15, wherein the aligning includesrubbing the alignment layer.
 17. The method claimed in claim 15, whereinthe aligning includes irradiating the alignment layer with light.
 18. Aliquid crystal display (LCD) device, comprising: a substrate; a colorfilter layer over the substrate; an overcoat layer over the colorfilter; and an alignment layer over the overcoat layer, whereinmaterials of the overcoat and alignment layers are separately formedfrom a single mixture of materials.
 19. A material mixture used infabricating a liquid crystal display (LCD) device including: a firstcomponent, the first component includes one of polyamide,polyimide-based compound, PVA, polyamic acid, PVCH, PSCN, and aCelCN-based compound; and a second component, the second componentincludes one of a photosensitive resin and a acrylic resin.
 20. Thematerial mixture of claim 19, wherein the first component is more densethan the second component.
 21. The material mixture of claim 19, whereinmixture contains more of the second component than the first component.22. The material mixture of claim 19, wherein mixture contains betweenabout 1% and about 10% of the first component.